Question: What happens to your body when you are freezing? I mean, how long can you last if you are freezing?

Helen Hanstock answered on 14 Nov 2016:

Great question Julia!

When our bodies get cold the first thing that happens is that the blood vessels in the extremities (e.g. fingers and toes) constrict so that heat is not lost from the blood and the warm blood can be used to keep our vital organs (e.g. heart and brain) warm.

Eventually if we are out in the cold for too long our core body temperature starts to fall. Our core body temperature is supposed to be kept at around 37C, and if it falls below 35C we call that hypothermia.

To start with you may start to feel tired, lose the ability to make decisions, lose coordination, and shiver a lot. Our muscles shiver because the activity generates heat and helps to keep us warm.

But if this still isn’t enough our core body temperature and skin temperature drops even further. If core body temperature drops below 31C we are in serious trouble! We stop shivering and may go into a state of ‘hibernation’. Our heart rate and breathing slow down, eventually our major organs stop working and the body is very close to death.

Depending on the situation, a few people manage to survive very extreme hypothermia if they are rescued and warmed up slowly and carefully. However, when we get very cold there is also a high risk of cardiac arrest (heart attack) which kills some people, and others die due to the cold/organ failure. How long we can last depends on the situation – particularly the rate of cooling. Water conducts heat away from the body much more quickly than air, and so if we are immersed in cold water then we may only be able to last 1-2 hours. In air it is possible to last much longer, depending on the temperature, wind chill and the amount of clothing you have. Typically once core body temperature gets below 31C we are in big trouble as the body and brain will not be functioning well enough to ‘self-rescue’. At 28C there is a very high risk of heart attack. We could get that cold perhaps in around 6-12 hours if we get wet or caught out in really bad weather without shelter.

Often when people die of hypothermia they show some strange behaviours just before they pass away – this can involve digging a hole or crawling into small spaces, and also taking clothes off because we suddenly ‘feel’ warm – this is thought to be due to a malfunction of the temperature sensor in the brain.